Agrin is an essential extracellular matrix component which promotes clustering of nicotinic acetylcholine receptors (nAChRs) and other proteins at the neuromuscular junction during development. Agrin, MuSK, and Rapsyn are all essential components for AChR aggregation, through an unknown mechanism. The C-terminal region of agrin is released into the medium, interacts with receptors on the muscle surface and induces AChR aggregation.

The diagram indicates the domain structure and functional regions of agrin, as well as domains required for AChR aggregation and alpha-dystroglycan and heparin binding.